Changing a baler from a fixed speed compressor motor to variable speed has saved a UK manufacturer £2800 p.a. in energy usage. Smurfit Kappa’s Northampton plant produces packaging such as fruit and vegetable trays, fresh produce boxes and retail-ready packaging. A hydraulic baler is used to compact off-cuts from the company’s cardboard processing lines into large bales ready for transport to a recycling plant.

The company wanted to improve the energy efficiency of the baler, which uses a fixed speed motor-driven pump to compress the hydraulic fluid. Another problem was overheating  due to  the high usage levels, and this resulted in installation of a motor-driven fan to keep it cool.

Monitoring the energy input of the baler showed that the measured power consumption was 11.1 kW and the baler ran for 6,336 hours. At an energy cost of 8p/kW hr, this gave an annual running cost of the baler of £5,626.

Lower energy use and improved environment

A 30 kW ABB UK general purpose ACS550 drive was installed on the motor and a pressure transducer added to the hydraulic circuit.  The pressure transducer gives a 4-20 mA output that is proportional to the pressure.  When the hydraulic ram is moving and fluid is flowing the pressure drops so the drive speeds up the motor to maintain pressure. When the ram is not moving, pressure rises so the ACS550 drive slows the motor.  As well as the energy saving aspect, the baler runs quieter and operates at a lower temperature.

Following installation of the variable-speed drive, the power consumption was measured again and shown to be 5.6 kW. This gave a reduced energy cost of £2,838 a year, a saving of £2,788, with a payback time of just over 17 months.

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